The present invention relates to an optical memory head for carrying out reproduction and/or recording of high density information by utilizing near-field light.
There has been used a scanning type probe microscope (SPM) such as a scanning type tunnel microscope (STM) or an atomic force microscope (AFM) for observing a very small region on the order of a nanometer on a surface of a sample. In the SPM, an image having a resolution dependent on a shape of a front end of a probe can be obtained by scanning the probe having a sharpened front edge above a surface of a sample with an interaction of tunnel current, atomic force or the like caused between the probe and the surface of the sample as an object of observation, however, a restriction imposed on the sample to be observed is comparatively severe.
Hence, at the present time, great attention has been given to a near-field optical microscope enabling observation of a very small region on a surface of a sample by using as an object of observation an interaction caused between near-field light formed at the surface of the sample and a probe by utilizing the propagating light.
According to a near-field optical microscope, propagating light is illuminated on a surface of a sample to thereby generate near-field light, the generated near-field light is scattered by a probe having a sharpened front end and the scattered light is processed similar to conventional propagating light detection by which a limit of a resolution of observation by a conventional optical microscope is exceeded and observation of a smaller region is made feasible. Further, by sweeping the wavelength of the light illuminated onto the surface of the sample, observation of optical physical properties of the sample in a very small region is also made feasible.
In the case of a near-field optical microscope, there is frequently used an optical fiber probe provided with a very small aperture at its front end and fabricated by sharpening an optical fiber and coating a surrounding thereof by a metal and scattered light produced by operating the optical fiber probe interactively with near-field light which is made to pass through an inner portion of the optical fiber probe and guided to an optical detector.
Further, observation of a surface can also be carried out by introducing light to a sample via an optical fiber probe to thereby generate near-field light at a very small aperture of the optical fiber probe and guiding scattered light generated by an interaction between the near-field light and a fine structure of a surface of the sample to an optical detector by using a focusing system added further.
Further, near-field light is not only utilized for a microscope but is applicable to high density optical memory recording in which near-field light having a high energy density is generated at a very small aperture of an optical fiber probe by introducing light having a comparatively large intensity to a sample via an optical fiber probe so that a structure or physical properties of a surface of the sample are locally changed by the near-field light.
As a probe used in a near-field optical microscope, for example, as disclosed in U.S. Pat. No. 5,294,790, there has been proposed a cantilever type optical probe in which a silicon substrate is formed with an aperture portion penetrating the substrate by semiconductor fabrication technologies of photolithography, etching, and so on, an insulating film is formed at one face of the silicon substrate and an optical waveguide layer having a conical shape is formed on an insulating film on the side opposed to the aperture portion. According to the cantilever type optical probe, an optical fiber is inserted into the aperture portion and light can be transmitted through a very small aperture formed by coating a metal film to other than a front end portion of a light guiding layer.
Further, there has been proposed use of a planar probe having no sharpened front edge as in the above-described probe. According to the planar probe, an aperture having a structure of an inverted pyramid is formed in a silicon substrate by anisotropic etching, particularly, an apex thereof is provided with a diameter of several tens of nanometers and penetrates the silicon substrate. According to such a planar probe, formation of a plurality thereof on the same substrate by using semiconductor fabrication technologies, that is, array formation is facilitated, particularly, the planar probe can be used as an optical memory head suitable for reproduction and recording of an optical memory utilizing near-field light.
However, the optical fiber probe is provided with the sharpened front end and accordingly, the mechanical strength is not sufficient, which is not suitable for mass production and array formation. Further, scattered light provided by disturbing near-field light is very weak and therefore, when the scattered light is detected after passing through an optical fiber, there is needed a device for providing a sufficient light amount at a detecting unit. Further, when a sufficient magnitude of near-field light is generated by passing through an optical fiber, there is needed a device for focusing light to a very small aperture portion of the optical fiber.
Further, according to the cantilever type optical probe, reception of scattered light from the light guiding layer and introduction of propagating light to the light guiding layer are achieved by inserting an optical fiber to the aperture portion and therefore, a sufficient light amount cannot be transmitted with no loss between the light guiding layer and the optical fiber.
According to the cantilever type optical probe, array formation, particularly array formation of a two-dimensional arrangement is difficult to realize. Further, an object of these was originally for use in a microscope and accordingly, no consideration was given to recording or reproduction of information in an optical memory and high speed sweep on a recording medium is difficult.
However, when the optical fiber probe, the cantilever type optical probe and the planar probe are used as optical memory heads, these probes are utilized only for either one of information recording and information reproduction as a premise. For example, when the optical fiber probe is used for recording information onto a recording medium, in order to reproduce information recorded on the recorded medium, there is needed a near-field light generating system for generating near-field light at a recording medium and a near-field light detecting system for scattering the generated near-field light and guiding the scattered light to an optical detector. Therefore, in order to realize high density information recording and reproduction by using such a probe, the constitution of the apparatus becomes complicated and the cost is also increased.
Further, when the optical fiber probe, the cantilever type optical probe and the planar probe are used as optical memory heads for reproducing information recorded on a recording medium, it is a normal practice that these probes are utilized only for either one of near-field light generating use for generating near-field light at a recording medium and near-field light detecting use for scattering the generated near-field light and guiding the scattered light to an optical detector and it is difficult to realize reproduction of information by use of only the probes of these types.
Further, according to the planar probe, in a state in which the very small aperture is made to proximate to a recording medium, sufficient space is not provided between the vicinity of the very small aperture and the recording medium and accordingly, there cannot be utilized near-field light of a reflected type for generating near-field light similarly at a surface of the recording medium by irradiating light to the surface of the recording medium.
Accordingly, it is an object of the invention to provide a near-field optical memory head having a compact constitution and suitable for mass production for realizing recording and reproduction of information of an optical memory utilizing near-field light. Further, it is another object thereof to provide a structure and means for easily taking out an optical signal.
According to a first aspect of the invention, there is provided a near-field optical memory head characterized as a near-field optical memory head for reproducing information on a recording medium by utilizing near-field light, the near-field optical memory head comprising a planar substrate formed by penetrating at least one hole in a shape of an inverted pyramid such that a top portion thereof constitutes a very small aperture, a light waveguide path formed in the planar substrate and a light source for making light incident on the light waveguide path, wherein one end portion of the light waveguide path is disposed at a side edge portion of the planar substrate and other end portion of the light waveguide path is disposed at an aperture edge portion of the very small aperture.
Therefore, formation of the near-field light by irradiating light from the side portion of the substrate to the recording medium via the light waveguide path and taking-out of the propagating light generated by the interaction of the formed near-field light and the very small aperture can be realized on the same substrate.
Further, according to another aspect of the invention, there is provided a near-field optical memory head, wherein the one end portion of the light waveguide path is disposed at an upper face portion of the planar substrate and a reflective layer for reflecting light passing through the light waveguide path is further formed at a portion of an inner side face of the light waveguide path.
Therefore, formation of the near-field light by irradiating light from the upper face of the substrate to the recording medium via the light waveguide path and taking-out of the propagating light generated by the interaction of the formed near-field light and the very small aperture can be realized on the same substrate.
Further, according to another aspect of the invention, there is provided a near-field optical memory head characterized in a near-field optical memory head for reproducing information of a recording medium by utilizing near-field light, the near-field optical memory head comprising a planar substrate formed by penetrating at least one hole in a shape of an inverted pyramid such that a top portion thereof constitutes a very small aperture, diffraction gratings formed on the planar substrate and at an edge portion of the hole and a light source for making illumination light incident on the diffraction gratings, wherein the diffraction gratings guide the illumination light to an aperture edge portion of the very small aperture via the planar substrate, the planar substrate comprises a material of transmitting the illumination light and a light shielding layer is formed at a surf ace of the very small aperture for emitting the illumination light except the aperture edge portion.
Therefore, formation of the near-field light by irradiating light from the upper face of the substrate to the recording medium via the diffraction gratings and taking-out of the propagating light generated by the interaction of the formed near-field light and the very small aperture can be realized on the same substrate.
Further according to another aspect of the invention, there is provided the near-field optical memory head characterized in a near-field optical memory head for reproducing information of a recording medium by utilizing near-field light, the near-field optical memory head comprising a planar substrate formed by penetrating at least one of holes in a shape of an inverted pyramid such that top portions thereof constitute very small apertures, diffraction gratings formed at a side end portion of the planar substrate and a light source for making illumination light incident on the diffraction gratings, wherein the diffraction gratings guide the illumination light to aperture edge portions of the respective very small apertures via the planar substrate, the planar substrate comprises a material for transmitting the illumination light and a light shielding layer is formed on surfaces of the respective very small apertures for emitting the illumination light except the aperture edge portions.
Accordingly, formation of the near-field light by irradiating light from the side face of the substrate to a plurality of different positions of the recording medium via the diffraction gratings and taking-out of the propagating light generated by the interaction of the formed near-field light and the very small aperture can be realized on the same substrate.
Further, according to another aspect of the invention, there is provided a near-field optical memory head characterized in a near-field optical memory head for recording and/or reproducing information of a recording medium by utilizing near-field light, the near-field optical memory head comprising a planar substrate formed by penetrating at least one hole in a shape of an inverted pyramid such that a top portion thereof constitutes a very small aperture, a light waveguide path formed along a side face of the hole in a depth direction, and light detecting means formed at one end portion of the light waveguide path, wherein other end portion of the light waveguide path is disposed at an aperture edge portion of the very small aperture and a light shielding layer is formed on a surface of the light waveguide path except the other end portion.
Therefore, introduction of the light waveguide path and reception at the light detecting means of the propagating light generated by interaction of the near-field light formed by irradiating light to the very small aperture and the recording medium, can be realized on the same substrate.
Further, according to another aspect of the invention, there is provided a near-field optical memory head characterized in a near-field optical memory head for recording and/or reproducing information of a recording medium by utilizing near-field light, the near-field optical memory head comprising a planar substrate formed by penetrating at least one hole in a shape of an inverted pyramid such that a top portion thereof constitutes a very small aperture, a lens formed at an aperture edge portion of the very small aperture, and light detecting means formed on an optical axis of the lens and on the planar substrate, wherein the planar substrate comprises a material of transmitting light and a light shielding layer is formed on a surface thereof except the lens portion.
Therefore, condensing by the lens and reception by the light detecting means of the propagating light generated by the interaction of the near-field light generated by irradiating light to the very small aperture and the recording medium can be realized on the same substrate.
Further, according to another aspect of the invention, there is provided a near-field optical memory head characterized in a near-field optical memory head for recording and/or reproducing information of a recording medium by utilizing near-field light, the near-field optical memory head comprising a planar substrate formed by penetrating at least one hole in a shape of an inverted pyramid such that a top portion thereof constitutes a very small aperture, wherein the planar substrate includes light detecting means at an aperture edge portion of the very small aperture and a light shielding layer is formed on a surface thereof except the light detecting means portion.
Therefore, reception by the light detecting means of the propagating light generated by the interaction of the near-field light generated by irradiating light to the very small aperture and the recording medium can be realized on the same substrate.
Further, according to another aspect of the invention, there is provided a near-field optical memory head for recording and/or reproducing information of a recording medium by utilizing near-field light, wherein near-field light forming means having a very small aperture portion for forming near-field light on the recording medium and near-field light detecting means for detecting the formed near-field light are provided on a same substrate and the substrate (hereinafter, referred to as a near-field light substrate) is constituted to project from a substrate at an outer peripheral portion.
Therefore, reception by the light detecting means of the propagating light generated by the interaction of the near-field light formed by irradiating light to the very small aperture and the recording medium, can be realized on the same substrate, further, the near-field optical memory head can easily approach the recording medium and an output signal can easily be taken out from an output terminal.